Conventionally, as a device for calculating traffic information, known is the one described in JP-A-11-328580.
The traffic information calculation device described in JP-A-11-328580 is configured by an vehicle mounted device and an information center as below.
The vehicle mounted device is mounted in a vehicle, and is provided with traffic information provision means that is configured to be able to automatically or manually provide the center with traffic information data about the area in the vicinity of the vehicle, and vehicle mounted device control means that exercises control to enable exchanging of the traffic information data with the center via wireless communication method.
The information center is provided with: database creation means that receives the traffic information data from the vehicle carrying therein the vehicle mounted device, and creates a traffic information database based on the received traffic information data; search means that searches, in response to a search request from the vehicle mounted device for the traffic information data of a predetermined region, the traffic information data of the predetermined region; and center-end control means that exercises control to forward the traffic information data of the predetermined region found by the search means to the vehicle mounted device that is a source of a transmission request for the traffic information data of the predetermined region.
With such a configuration, in the traffic information calculation device described in JP-A-11-328580, the information center collects the traffic information data about the area in the vicinity of the vehicle carrying therein the vehicle mounted device, creates a database, and provides the vehicle with any needed traffic information data in response to a request coming from the vehicle.
Herein, the traffic information data also includes data about waiting time at intersections to make right or left turn, for example. For calculation thereof, the vehicle mounted device produces, as a waiting time for right or left turn, the time duration when the vehicle speed is at a given speed or slower with the turn signal turned on, and transmits the result to the information center. Based on the result, the information center calculates an average value of the waiting time for right and left turns, and provides the calculation result as a part of the traffic information data to the vehicle being the source of the request.
Moreover, conventionally, as a method for an vehicle mounted device to display traffic information, known is the one described in JP-A-2004-234649.
In the traffic-information display method described in JP-A-2004-234649, an vehicle mounted navigation device accumulates congestion information coming from a traffic information provision center or vehicles, and creates congestion statistical information through statistical analysis performed on the information about a specific road interval for every season, every day of a week, and others. The navigation device acquires the resulting traffic congestion statistical information for display of a map on the screen.
This enables the navigation device to display, on the map, frequent points of traffic congestion on the road through with statistical analysis, average level of traffic congestion thereon, occurrence time of traffic congestion thereon, and others, and eases users to make their decisions to avoid traffic congestion.
The problem with the conventional traffic information calculation device described in JP-A-11-328580 is that, although information about making right and left turns at intersections is indeed acquired, the branch direction is determined only whether the turn signal is on or off, and therefore there is a difficulty in knowing if the branch direction is toward the front right, toward the far right, or others. If with a complicated-shaped intersection of five or more roads, e.g., five- or six-forked road, it is almost impossible to know the specific branch direction, resulting in the problem of not being able to correctly represent intersection traffic information for every branch direction.
The problem with the conventional traffic information calculation device described in JP-A-11-328580 is that, although the information center is using information about turn signals coming from vehicle mounted devices to perform statistical analysis on the traffic congestion information, every vehicle mounted device is not always provided with the function of transmitting information about the turn signals as of this point in time. It thus means that the information center is not always having the information about the turn signals of every vehicle mounted device, and there is a limitation for the data available for collection by the information center, thereby leading to a problem of not being able to have correct information.
Moreover, in the conventional traffic information calculation device described in JP-A-11-328580, an vehicle mounted device itself is provided with means for calculating the data about the waiting time at intersections. With such a configuration, if the information center wants to have all information including the turn signal information from the vehicle mounted devices, there needs to make improvements to those vehicle mounted devices, e.g., provide means to every vehicle mounted device for calculating the data about the waiting time at intersections, or provide means thereto for detecting the turn signal information. As such, there is a problem of not being able to use the current vehicle mounted devices without making improvements thereto.
Furthermore, with the traffic-information display method described in JP-A-2004-234649, although information about the road through with statistical analysis can be indeed displayed on the map, e.g., frequent points of traffic congestion, average level of traffic congestion, and occurrence time of traffic congestion, the traffic congestion information is not displayed in accordance with the branch direction, e.g., the traffic congestion information does not tell which branch direction at an intersection is congested, or if congested, the level of congestion of the direction. This results in the problem that the users cannot make their determinations, to their perfect satisfaction, to avoid the traffic congestion.